Therapeutically useful targeting of human neoplasia requires selective disruption of specific pathway functions in established cancers without destruction of normal tissue. The Erk MAPK pathway is a highly conserved signaling cascade that is aberrantly activated in approximately one third of human cancers and in the majority of squamous cell cancers (SCC). In addition, the combination of Erk MAPK cascade activation with G1 cell cycle escape can transform normal human epidermis into SCC. As such, this pathway remains a promising target for cancer therapeutics. Unfortunately, recent work from our laboratory revealed that ablation of Erk MAPK cascade signaling at the level of both Mek1/2 and Erk1/2 not only blocked Ras/Raf driven neoplastic changes but also resulted in growth inhibition and destruction of the surrounding epidermis. These studies highlight the importance of finding methods to target MAPK function selectively in cancer without disrupting normal skin. One promising method of achieving selective inhibition of the Erk MAPK pathway is through targeting MAPK-interacting proteins (MAPK-IPs). MAPK-IPs bind to the core kinases of the Erk MAPK pathway serving as scaffold, adaptor and regulatory proteins and thereby alter pathway output. IQ motif-containing GTPase activating protein 1 (IQGAP1) is a MAPK-IP that binds all Mek and Erk isoforms and enables Erk MAPK activation in specific settings. We recently showed that targeting IQGAP1 selectively blocks early epidermal carcinogenesis without disrupting homeostasis in normal epidermal tissue. The goal of this Ruth L. Kirschstein NRSA Postdoctoral fellowship application is to determine the role of IQGAP1 in established epidermal tumors and to define the functional domains of IQGAP1 required for Erk MAPK-driven epidermal neoplasia. In AIM I, we will develop a series of mutants lacking each known domain the IQGAP1 protein and determine if these mutants retain the ability to support Erk-MAPK driven epidermal transformation. In AIM II, we will functionally assess the requirement for IQGAP1 on the sustenance of invasive epidermal tumors. siRNAs and shRNA expression retrovectors will be used to target IQGAP in invasive epidermal tumors and the effect of IQGAP1 depletion on tumor sustenance will be evaluated. At the end of the proposed funding period, we hope to have defined the IQGAP1 domains responsible for tumorigenesis and to have defined where in the carcinogenesis spectrum it acts. PUBLIC HEALTH RELEVANCE: This proposal aims to identify and characterize therapeutically useful targets which selectively block Erk MAPK signaling in epidermal tumors but not in homeostasis and thereby aid in the development of future cancer therapeutics.